Aural stroboscope



x sept. 26, 1939.

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D. JouRNEAux Ir A1. 2,174,176

AURAL STROBOSCOPE Filed Sept. 23, 1956 Ammunlamented epi. 26, 1939 ,une

UNITED STATES PATENT OFFICE AURAL STROBOSCOPE Didier Journeaux,Wauwatosa, and Samuel R.

Durand, Milwaukee, Wis., assignors to Allis- Chalmers ManufacturingCompany, Milwaukee, Wis., a corporation of Delaware ApplicationSeptember 23, 1936, Serial No. 102,102

6 Claims. (Cl. 73-51) This invention relates in general to stroboscopes,and more particularly to an instrumentI for indicating or recordingvibrations which may not readily be detected visually.

provide a device for observing vibrations produced at the differentmoments of the operating cycle of a moving mechanism.

Another object of the present invention is to It is well known that themovement of a provide a device for determining the moment mechanismhaving a regular cycle of operation of the operating cycle of a movingmechanism may be observed and analyzed visually by means at which anyparticular vibration takes place of stroboscopes which illuminate themechanism therein. at a predetermined moment in each cycle of Anotherobject of the present invention is to operation thereof. In such manner,it is possible provide a device for observing the position of a toobserve the operation of such mechanisms as moving mechanism at which aparticular vibrainternal combustion engines, electric motors, gear tiontakes place therein. trains, etc. in which vibrations or other irregu-Objects and advantages other than those above larities of motion may bedetected and analyzed, set forth will be apparent from the followingdeprovided that such irregularities occur in a por` scription when readin connection with the ac tion of the mechanism which is visible andwhich companying drawing, in which:

may be illuminated, and provided that such Fig. 1 diagrammaticallyillustrates one emirregularities be of visible magnitude. Such bodimentof the present invention in which the method however does not permitdetermination occurrence of a vibration in a moving mechanism of theorigin of vibrations of smaller magniis correlated to the position ofthe mechanism as tudes, including vibrations of audible frequencyindicated on a dial; and

or so-called machinery noises, which are fre- Fig. 2 diagrammaticallyillustrates another quently an indication of faulty operation andembodiment of the present invention in which which may also beobjectionable per se. -Such the position of a moving mechanism isobserved 35 noises may result from lost motion between memonly at thetime of occurrences of a predeterbers in mechanical engagement, or fromvariamined vibration. tions in the relative position of members in con-Elements performing the same functions in tact with a now of fluid, suchas the xed and the two embodiments shown are designated moving vanes4,of pumps, blowers or turbines of therein by the same referencenumerals. It will 30 the rotary type, or such as the pole pieces and beunderstood that elements illustrated in one the armature slots of dynamoelectric machines. of the ligures 0f the draWing may alSO be 00in-Although such noises may be observed by bined with elements illustratedin the other hearing, it is not always possible to separately ligure t0form further embodiments 0f the inrecognize different noises occurringintermitvention.

35 tently during different portions of the operating Referring moreparticularly to the drawing by cycle of the mechanism under observationand, characters of reference, reference numeral 6 if such cycle isrepeated a large number of times designates the mechanism such as aninternal per second, it is not possible to determine at Combustionengine, Which it iS desired t0 0bwhich moment of such cycle a particularnoise serve in Operation. Vibrations 0f audible and 40 occurs. Analysisof such noises may be 0bother frequencies produced in the engine aretained by impressing the vibrations to be anadetected by means of asuitable vibration responiyzed on a transmitting device, converting suchsive device, Such as a microphone l of any suitvibrations into electriccurrent, and subjecting able type adapted t0 be subjected t0 theVibration an indicating or recording device to the eiTect produced bythe engine. The IniCrODhOne iS 45 of such current only at predeterminedmoments illustrated aS being 0f the CaIbOn granllle type,

in the operating cycle of the mechanism under and iS suitably arrangedWith I'eSPeCt t0 engine 6- observation. The actuaI position of themecha- For example, the microphone may be Supported nism at suchpredetermined moments may then independently 0f engine 5 and fOCuSedtOWard also be observed visually by means of a visual anlr particularDOrtOn 0f the engine, but to 50 stroboscope, obtain the greatestpossible response of the Itis, therefore, one of the objects of thepresmicrophone to the vibrations of engine 6 the ent invention toprovide a device for isolating body of the microphone is rigidly mountedon vibrations produced at a predetermined moment any desired part of theengine to follow the of the operating cycle of a moving mechanism.movements thereof, the vibrations of contact 55 Another object of thepresent invention is to resistance of the'carbon granules resulting fromthe inertia of such granules. The microphone is associated with suitablemeans such as a circuit comprising a battery 8 and a transformer 9,connected therewith for producing an electric current in response to theamplitude and frequency of the vibrations impressed on the microphone. Acurrent indicating device is suitably connected with transformer 9 tooperate in response to the variations of the flow of current through themicrophone. Such device may be an electric meter of the indicating or ofthe recording type, or an oscillograph, and if only audible vibrationsare to be detected the device may be a telephone receiver Il.

In general, the output energy of transformer 9 is too low to cause theproduction of a sufficiently audible signal in receiver I I. It istherefore preferable to include in the current producing means anamplifier, generally designated by I2, provided with input terminalsconnected with transformer 9 and with output terminals connected withreceiver II. The amplifier may be of any of the known types, andpreferably comprises three electric valves I3, I4, I6 of the screengridhigh vacuum type each having an anode, a control grid, a screen-grid anda cathode. The cathode filaments of all three valves may be energizedfrom a common source, such as a battery I1, through an adjustablerheostat I8, and the three valves are provided with a common platebattery I9 connected with the cathodes of the valves through a tappedrheostat 2I serving as source of bias potential for the control grid ofvalve I6. Rheostat 2I is connected in parallel with a capacitor 22serving to by-pass alternating current from the rheostat. Thescreen-grids of the valves are severally connected with the associatedcathodes through capacitors 23, and are connected with the positiveterminal or with an intermediate point of battery I9 through resistors24. The control grid of valve I3 is connected with the associatedcathode through the secondary winding of transformer 9 and through abias battery 26. The control grid of valve I6 is connected with theassociated cathode through a portion of rheostat 2| and through thesecondary winding of a transformer 21 having the primary winding thereofinserted in series with a resistor 28 in the plate circuit of valve Ill.Receiver II is connected in the plate circuit of valve I6 to receive theoutput current of the amplifier and to translate such current intoaudible vibrations.

The operation of receiver II is controlled by means such as a switch 29controlling the amplitude of the output current of amplifier I2, adaptedto be actuated in synchronism with the mechanism 6. Switch 29 ispreferably of the contactor type comprising a rotary conductive drum 3Icooperating with a fixed brush 32, the drum being covered with a layerof insulation interrupted at one point by a single conductive segment.The drum is adapted to be driven in synchronism with engine 6 in anysuitable manner, such result being preferably obtained by connecting thedrum with the shaft of the engine. Such connection may be effecteddirectly to cause switch drum 3l to make one revolution for eachrevolution of the shaft of engine 6, or may be made through gears 33, ifengine 6 is of the four-cycle type, to cause drum 3| to make onerevolution for every two revolutions of the engine shaft. The positiono-f the shaft of engine 6 corresponding to the engagement of brush 32with the segment of drum 3l may be varied by displacing brush 32 aboutdrum 3I by means of a lever 34 of which the posigui tion may beindicated by a pointer on a scale 3B. Switch 29 connects the controlgrid of valve I4 with the associated cathode through a source ofnegative potential such as the battery 31, another connection betweenthe grid and the cathode being established through a source of potentialless negative than the potential of battery 31, such as a battery 35 anda resistor 40.

In operation, engine 6 whether operating at a constant or variablespeed, is subject to complex vibration of different amplitudes andfrequencies including audible frequencies, such vibrations beingproduced at different moments in the cycle of operation of the engine.During the successive passages of the shaft of the engine through one ofcertain particular positions, the engine produces a certain periodicallyintermittent vibration. Assuming that it is desired to observe thenature and condition of occurrence of such certain vibration, it isnecessary tgwidsolate it from `pther vibrations interviwngbetween the dsgoclciirrncj 'the'roff 'll the engine vibrations areimpr'ss'ed'onmi'crophone 1, and a corresponding current iiows throughthe microphone and through the primary of transformer 9, the outputvoltage of the transformer being amplified by valves I3 and I6 and beingimpressed on receiver Il. To isolate any vibration, switch 29 isoperable in synchronism with the periods of occurrence of such vibrationto close the circuit thereof during such periods to thereby control theoperation of amplifier I2. The control grid of valve Ill is thusmaintained momentarily at a predetermined negative potential withrespect to the associated cathode by means of battery 31, the voltage ofthe battery being so chosen that valve Ill is then substantiallynon-conductive and has no material effect on the operation of valves I3and I6. During the intervening periods, the control grid of valve I4 ismaintained at another potential with respect to the associated cathodeby means of battery 35. The voltage of battery 35 is so chosen that,during such intervening periods, valve I4 is materially conductive andthus periodically substantially short circuits valve I3 which isconnected in parallel thereto through the primary winding of transformer21, thus rendering valve I3 intermittently inoperative to amplify thecurrent of microphone 1. It will be understood that valve I4 need notprovide a path of substantially zero impedance across valve I3, butneeds only draw a flow of current such that 'the greater portion of thevoltage of battery I9 appears across resistor 28, the residual voltageimpressed across the anode and the cathode of Valve I3 being reducedbelow the value necessary for rendering valve I3 operative.

Amplifier I2 is thus rendered operative only at predetermined moments ofeach cycle of operation of engine 6, i. e. during the occurrence of thevibration under consideration, and is otherwise inoperative. Receiver II is thus subjected to the effect of the electric current of microphone1 only during the periods of occurrence of the predetermined vibration.By moving lever 34, switch 29 may be caused to close at any desiredmoment of the cycle of the operation of engine 6 and it is thus possibleto isolate vibrations occurring in the engine at any particular momentofthe operating cycle thereof. The point of such cycle at whichthevibration detected in receiver II occurs is indicated on scale 36,which may be calibrated in angularV positions of the crankshaft of theengine. Bycontrolling the operation of amplifier I2 by means of valveI4, switch 29 is not inserted directly in the amplifying circuit, andthe closing and opening of such switch does not introduce any transientsin the current of receiver II. If such transients are of toc smallmagnitude to be objectionable, or if they may be readily distinguishedfrom the vibrations of the engine, a simpler arrangement may beutilized, as shown in Fig. 2.

In the embodiment illustrated in Fig. 2, microphone 1 is assumed to besubjected to audible vibrations transmitted thereto through air by apair of gears 38, such gears transmitting energy between an electricmotor 39 and an energy consuming device such as a brake 4 I. In thepresent embodiment, amplier I2 comprises a single electric valve of thethree electrode high vacuum type controlling the flow of current betweenbattery I9 and receiver II. The grid of valve 42 is connected with theassociated cathode through a source of negative potential such as abattery 43 and through a resistor 44 to normally maintain the valvesubstantially non-conductive. Switch 29 is preferably actuated insynchronism with gears 38 by driving drum 3I from motor 39, and isutilized for connecting the grid of Valve 42 with the associated cathodeindependently of battery 43 through a source of potential such as abattery 46 less negative than the potential of battery 43, to rendervalve 42 conductive to an extent depending on the action of transformer9, and to thus render the amplifier operative. Switch 29 is actuatedsimultaneously with another switch 41 forming part of a visualstroboscope 48. The stroboscope may be of any type known in the art andmay comprise a source of direct current, such as a battery 49, adaptedto charge a capacitor 5I through a resistor 52 and a reactor 53. Thecapacitor may be periodically discharged through a mercury vapor lamp 54serving to illuminate gears 38 during movement thereof in response toeach closure of switch 41. Such result is obtained by charging anothercapacitor 51 from battery 49 and by utilizing the switch for controllingthe grid of a vapor electric valve 56 to cause valve 56 to periodicallydischarge capacitor 51, through an inductive circuit. Such dischargesare used for impressing potential impulses on the starting band olf lamp54. Lever 34 is utilized for simultaneously adjusting the operation ofswitches 29 and 41 with respect to the operating cycle of gears 38 tocause the stroboscope to illuminate gears 38 during the periods ofoperation of amplifier I2.

With the arrangement diagrammatically illustrated in Fig. 2, vibrationsof gears 38 appearing as noises transmitted to microphone 1 arecontinuously translated into electric current flowing throughtransformer 9. Battery 43 generally maintains valve 42 substantiallynon-conductive and receiver I I is thus generally without current.During each closure of switch 29 battery 46 overcomes the action ofbattery 43 and renders valve 42 conductive to an extent depending uponthe action of transformer 9. Receiver I I thus indicates the noiseproduced by gears 38 only during successive passages of a pair ofcooperating teeth of the gear through a particular relative position, inwhich position the gears are illuminated by stroboscope 48. By movinglever 34, such position may be varied for observing the diierent pointsof the entire period of engagement of any pair of teeth of the gears. Ifdesired, switches 29 and 41 may be actuated at such speed as'to closeonce during the engagement of each pair of teeth of gears 38, to hearthe average amount of noise produced by the gears at each point of theengagement of all the teeth thereof, and to render visible the averagemotion of such teeth at each such position.

Although but two embodiments of the present invention have beenillustrated and described, it will be apparent to those skilled in theart that various changes and modications may be made therein withoutdeparting from the spirit of the invention or from the scope of theappended claims. y

It is claimed and desired to secure by Letters Patent:

1. A device for isolating vibrations produced by a movingmechanismjhaving a periodic cycle of operation, comprisingrieans'includinga. microphone adapted to be subjected to vibrations bythe mechanism for translating the vibrations into electric current, anamplifier having input terminals connected with said vibrationtranslating means and comprising an electric valve having a cathode anda control grid, a source of current connected between said cathode andsaid grid to maintain said valve non-conductive, a switch adapted to beactuated in synchronism With the mechanism for connecting said grid withsaid cathode independently of said source to render said valveconductive, means for adjusting the operation of said switch withrespect to the operating cycle of said mechanism, whereby said amplieris rendered operative only during closure of said switch, means forindicating the adjusted position of said switch, and an indicatingdevice connected for receiving current from said amplifier.

2. A device for isolating vibrations produced by a moving mechanismhaving a periodic cycle of operation, comprising means includingarnicrophone adapted to be subjected to vibrations y he mechanism fortranslating the vibrations into electric current, an amplifier havinginput terminals connected witl'sidwibration translating means and havingoutput terminals, an indicating device connected with the outputterminals of said amplier, a switch for controlling the operation ofsaid amplier, a strobpspppe including another switch for intermittentlyillm'- nating the mechanism, means for simultaneously actuating saidswitches in synchronism with the mechanism, means for adjusting theoperation of said switches with respect to the operating cycle of themechanism, and means for indicating the adjusted position of saidswitches.

3. A device for isolating vibrations produced by a moving mechanismhaving a periodic cycle of operation, comprising means including amicrophone adapted to be subjected to vibrations by the mechanism fortranslating the vibrations into electric current, an amplier havinginput terminals coupled with said vibration translating means andcomprising an electric valve, a second electric valve for periodicallyby-passing the rst said valve to render the rst said valve inoperative,means comprising a switch actuable in synchronism with said mechanismfor controlling the conductivity of the said second electric valve,means for adjusting the operation of said switch with respect to theoperating cycle of said mechanism, and means for indicating the adjustedposition of said switch.

4. In combination, a microphone subjected to recurring successions ofvibrations of diiTering characteristics including an intermittentvibration having a particular characteristic, means comprising anelectric valve coupled with said microphone for producing electriccurrent in re- .a We

10 mittent vibration for controlling the conductivity of said valve insuch sense as to render the said current producing means operative onlyduring the periods of said intermittent operation, and means forindicating the adjustment of the sec- 15 ond said means.

5. An apparatus for testing a machine having a rotary member, toselectively determine the frequency and angular location relative tosaid xfa...

rotary member Y`oiperiodic noises produced by said machine; comprising amicrophone responsive to said noiseseior producing electric currentVariations, a frequency indicator electrically coupled to saidmicrophone, an intermittent electric switch actuated by said rotarymember for rendering said indicator effective at periodic intervals, andmeans for adjusting the effective position of the switch relative to theangular position of said member, to thereby adjust the time at whichsaid indicator is rendered effective.

6. The apparatus recited in claim 5, a stroboscope operable by saidrotary member and means for adjusting said stroboscope in unison withsaid switch.

DIDIER J OURNEAUX. SAMUEL R. DURAND.

CERTIFICATE 0F CORRECTION. Patent `No .-1 2,17LL,1'Z6. September 26,1959. ,5, S DIDIER JCURNEAUX, ET AL.

y) Itvis hereby certifiedthat error appearsin the -printedSpeeifioa'tion of the above'numbered patent requiring Correction asfollows:V Page h., first Colmn, line .5, `claim LL, for the word "said"read such; and that the said Letters Patent should be read with thiscorrection therein 'that the same may -conform to Athe reoord` ofvthecase 'in the Patent Office.

Signed and sealegthig` Zbrth lay of Ootober, A. D. 1959,l

Henry Van Arsd'ale, (Seal) Acting Commissioner of Patents.

